Generally, an air ventilator is actuated as a contrary concept to an electric fan and must be located at an opening which leads to the outside, because a ventilator is intended to purify the interior of a room by drawing out the turbid air therefrom. However, since a ventilator is located at an opening which leads to the outside, worms or dirty air tends to flow backward through and between the ventilator blades. To solve these disadvantages, a device having blades for blocking the air-passage has been provided. However these prior art devices also have many disadvantages such as increased stream friction of the air by the blades disposed in front of the air-passage and a reduction in air ventilation efficiency. As a result, the air ventilator device must be operated for long periods of time and it is necessary to block the air-passage when it is not operating by a separate means like a blade.